1. Field of Invention
The invention relates to an engine fuel additive and fuels containing the inventive additive. This additive is characterized in that it exhibits improved low temperature solution properties as well as improving fuel economy.
2. Background of the Invention
Government legislated fuel economy standards have resulted in efforts being made by both automotive and additive suppliers to enhance the fuel economy of motor vehicles. One approach to achieve greater fuel efficiency is by lubricant formulation. Fuel consumption can be reduced either by decreasing the crank case oil viscosity or by reducing friction at specific, strategic areas of an engine. For example, inside an engine, about 18% of the fuel""s heat value is dissipated through internal friction (bearings, valve train, pistons, rings, water and oil pumps) while only about 25% is actually converted to (useful) work at the crankshaft. The piston rings and part of the valve train account for over 50% of the friction and operate at least part of the time in the boundary lubrication mode during which a friction modifier (FM) may be effective. If a friction modifier reduces friction of these components by a third, the friction reduction corresponds to about a 3.0% improvement in the use of the fuel""s heat of combustion and will be reflected in a corresponding fuel economy improvement.
A chemical additive designed to improve engine fuel economy is disclosed in U.S. Pat. No. 4,729,769, the contents of which are hereby incorporated by reference. This Patent discloses an additive which is obtained by the reaction of a C6-C20 fatty acid ester and a mono- or di-hydroxy hydrocarbon amine. Specifically, the additive is obtained by the reaction of 0.8 moles of coconut oil with 1.44 moles of diethanolamine (representing a molar ratio of coconut oil to diethanolamine of 0.555) by heating it at 120xc2x0 C. to 150xc2x0 C. for between 2 and 4 hours. Fuel economy is improved when this reaction product mixture is used as a gasoline or diesel fuel additive.
However, the limited temperature solution stability of this product is not as advantageous as desired. Thus, a problem encountered with such additives is due to their poor low temperature stability. Such additives are typically produced at a chemical plant which is remote from the petroleum terminal where the additive is blended with the fuel, e.g., gasoline or diesel fuel, prior to delivery to service stations. The additive must therefore be shipped from the manufacturing facility to a terminal by tank, truck or rail car. Once the additive arrives at the terminal, it is typically stored in a tank from which it is pumped and blended with gasoline stocks. The duration of shipment and storage of the additive can last several days to a year during which time the temperature of the fuel can reach very low temperatures, e.g., 10xc2x0 F. or lower. It has been observed that prior art additives often precipitate or produce a flocculent sediment while stored at such low temperatures. This instability at lower temperatures is highly adverse to the quality and efficiency of the additive and thus impairs the ability to use the additive.
We have discovered a novel fuel additive which exhibits substantially improved low temperature solution properties and yet performs at least as well as presently known friction modifier additives.
More particularly, we have discovered that the foregoing improvements can be Achieved by utilizing as a fuel additive, a composition comprising the reaction product of a reaction mixture composed of:
a) mixed fatty acid esters;
b) a mono or di-(hydroxy alkyl amine) or mixtures thereof; and
c) a low temperature property enhancing effective amount of a low molecular weight ester;
wherein the reaction mixture has a molar ratio of amine to total ester content in the range from 10.0 to 1.0.
In addition, we have found that the inventive composition is obtained by heating:
a) mixed fatty acid esters;
b) a mono or di-(hydroxy alkyl amine) or mixtures thereof; and
c) a low temperature property enhancing effective amount of a low molecular weight ester;
The amounts of each component and the temperature and the time period of heating being sufficient to produce an amide to ester absorbance ratio in the composition of at least 2.0 as measured by transmission infrared spectroscopy.
The first component used to produce the inventive composition may be a mixed ester of fatty acids containing 6 to 20, preferably 8 to16 carbon atoms. These acids may be characterized by the formula RCOOH wherein R is an alkyl hydrocarbon group containing 7-15, and preferably 11-13 carbon atoms.
The mixed ester may be a tri-ester, such as, a glycerol tri-ester of structural formula I: 
wherein R, Rxe2x80x2, and Rxe2x80x3 are mixtures of aliphatic, olefins, or polyolefins.
Typical of the mixed fatty acid esters which may be employed may be the following:
glyceryl tri-laurate
glyceryl tri-stearate
glyceryl tri-palmitate
glyceryl di-laurate
glyceryl mono-stearate
ethylene glycol di-laurate
pentaerythritol tetra-stearate
pentaerythritol tri-laurate
sorbitol mono-palmitate
sorbitol penta-stearate
propylene glycol mono-stearate
These esters may include those wherein the acid moiety is a mixture such as is found in natural oils typified by the following oils:
Coconut
Babassu
Palm kernel
Palm
Olive
Caster
Peanut
Rape
Beef Tallow
Lard (leaf)
Lard Oil
Whale blubber
The preferred mixed ester is coconut oil which contains the acid moieties summarized Tables 1 and 2.
The second component used to produce the inventive composition may be a primary or a secondary amine which possesses a hydroxy group characterized by formula II:
HN(Rxe2x80x2xe2x80x3OH)2-aHaxe2x80x83xe2x80x83(II) 
wherein Rxe2x80x2xe2x80x3 is a divalent alkylene hydrocarbon group containing 1-10 carbon atoms, and a is 0 or 1.
Typically amines may include ethanolamine, diethanolamine, propanolamine, isopropanolamine, dipropanolamine, di-isopropanolamine, butanolamines, and the like. Preferred is diethanolamine, CAS Number (111-42-2) which is a basic alkanolamine containing reactive appendages at each of its three termini. Its structural formula is shown as (III). 
The third component used to produce the inventive composition is a low molecular weight ester which imparts the enhanced low temperature properties of the resultant composition. The low molecular weight ester has an acid moiety represented by the formula:
Rxe2x80x3xe2x80x3COxe2x80x94
wherein Rxe2x80x3xe2x80x3 is an alkyl or alkenol hydrocarbon group containing from about 3 to 10 carbon atoms. Preferably, the acid moiety of the low molecular weight ester is selected from the group consisting of aprylic, caproic, capric and mixtures thereof. Most preferably, the low molecular weight ester is methyl caprylate, also known as methyl octanoate, CAS Number (111-11-5). It is the ester obtained from the reaction of octanoic acid and methyl alcohol and has the structural formula depicted as IV:
CH3(CH2)5COCH3xe2x80x83xe2x80x83(IV) 
Preferably the inventive composition is prepared from a reaction mixture in which the molar ratio of amine to total ester is in the range from about 8.0 to 2.0. The amide to ester absorbance ratio of the inventive composition is in the range from at least about 2 as measured by transmission infrared spectroscopy.
The mixture is heated for a time period of about from 0.5 to 10.0 hours and at a temperature at from about 60xc2x0 C. to about 250xc2x0 C. to produce the inventive composition which exhibits enhanced properties. Typically, the mixture is heated at a temperature of from about 60xc2x0 C. to about 200xc2x0 C. for a time period of from about 0.5 to 10 hours. Preferably, the mixture is heated for a time period of from about 1.5 to about 6.0 hours, and most preferably at a temperature in the range from about 110xc2x0 C. to about 180xc2x0 C.
A preferred reaction mixture is composed of from about 0.1 to about 0.8 moles of the mixed fatty acid ester, from about 1.0 to about 4.5 moles of the amine and from about 0.01 to about 0.60 moles of the low molecular weight ester. Most preferably, in the reaction mixture, the amount of fatty acid ester mixture is in the range of from about 0.5 to 0.8 moles, the amount of the low molecular weight ester is in the rage of from about 0.1 to about 0.5 moles, and the amount of the amine is in the range of from about 1.2 to about 3.2 moles.
In the final fuel additive composition, the molar ratio of the amine to total ester content is in the range of from about 5.0 to 2.2, wherein the term xe2x80x9ctotal ester contentxe2x80x9d means the combined molar amounts of the mixed fatty acid ester and the low molecular weight ester.
When added to a fuel, the inventive composition exhibits friction modifying and detergent properties at least as good as those exhibited by prior art compositions, such as the composition exemplified in U.S. Pat. No. 4,729,769. However, in addition, it exhibits improved stability at low temperatures, such as, those temperatures that may be encountered during shipping of the composition.
When used in a fuel composition, the base fuel in which the inventive fuel additive composition may be used may be a motor fuel composition composed of a mixture of hydrocarbons boiling in the gasoline boiling range or the diesel fuel boiling range. This base fuel may contain straight chain or branch chain paraffins, cycloparaffins, olefins and aromatic hydrocarbons as well as mixtures of these. The base fuel may be derived from straight-chained naptha, polymer gasoline, natural gasoline, catalytically cracked or thermally cracked hydrocarbons as well as catalytically reformed stocks. It may typically boil in the range of about 80xc2x0 to 450xc2x0 F. and any conventional motor fuel base may be employed in the practice of the invention.
The fuel composition of the invention may also contain any of the additives normally employed in a motor fuel. For example, the base fuel may be blended with anti-knock compounds, such as tetraalkyl lead compounds, including tetraethyl lead, tetramethyl lead, tetrabutyl lead, and/or cyclopentadienyl manganese tricarbonyl, generally in a concentration from about 0.05 to 4.0 cc. per gallon of gasoline. The tetraethyl lead mixture which is commercially available for automotive use contains an ethylene chloride-ethylene bromide mixture as a scavenger for removing lead from the combustion chamber in the form of a volatile lead halide. The motor fuel composition may also be fortified with any of the conventional additives including anti-icing additives, corrosion-inhibitors, dyes, etc.
The fuel additive composition may be added to the base fuel in minor amounts sufficient or effective to produce a detergent and friction reducing property to the mixture. The additive is particularly effective in an amount of about 0.002 to 0.2 wt. % (ca. 0.6 to 64 PTB) (PTB stands for pounds per thousand barrels). The preferred range is from about 0.008 to 0.1 wt. % (ca. 2.7 to 34 PTB), and most preferably, about 0.02 to 0.08 wt. % (ca. 6.4 to 27 PTB). (All wt. % is based on the total weight of the fuel composition.
Experimental Section.